Electron discharge apparatus



1932- K. c. DE WALT v ELECTRON DISCHARGE APPARATUS Filed Oct. 8, 1929600 /000 I200 I400 I600 /800 2000 2200 FLA TE VOL 734 6E VOL TS 200 300FIELD smsuarm GAUSSES Inventor: Kenneth C. De Walt,

His Attorrweg.

Patented Nov. 29 1932 UNITED. STATES.

PATENT oaFIcE KENNETH C. DE WALT, OF SCHENECTA DY, NEW YORK, ASSIGNOR TGENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK ELECTRON DISCHARGEAPPARATUS Application filed October 8, 1929. Serial No. 398,249.

The present invention relates to the construction and operation ofelectron discharge apparatus and more particularly to devices in whichthe direction and flow of electrons are controlled by combined magneticand electrostatic fields in such amanner as to produce a'negativeresistance characteristic, indicative of the ability to produceamplification or oscillations when connected in appropriate circuits.

Apparatus ofthis character may comprise a source of electrons and one ormore pairs of symmetrically arranged electron receiving surfaces, thetravel of electrons being directed by a suitably applied electrostaticfield and r a supplementary magnetic field. The elec- E. vol. 16, June1928, pp. 735-6, and by K.

tron receiving surfaces constitute anodes which usually take the form ofsegments of a cylinder, while the source of electrons con sists of afilament disposed in the: longitudinal-axis of the cylinder. A device ofthis sort may be termed, for convenience, a split anode magnetron andexamples of such construction are described by H.Yagi in an articleentitled Beam transmission of ultra short waves appearing in Proc. ofthe I. R.

Okabe in an article entitled On short Wave limit of magnetronoscillations appearing in the Proc. of the I. R. 15., vol 17, April1929, p. 652-659 inclusive. It is stated in these disclosures that thesplit anode magnetron ofi'ers an advantage over'electrostaticallycontrolled electron discharge devicesin that the interelectrode capacityis comparatively small and hence when the device is con-. nected insuitable circuits, oscillations of short wave lengths and ofconsiderable amplitude may be generated.

' In the usual form of split anode magnetron, the filament constitutes asingle leg of substantially the same length as the anode and when it isdesired to increase the filament emission for higher power output, ahairpin or spiral may be used in order to maintain the proper length offilament. The present invention is directed more particularly tothemanner in which .a filament of the hairpin type may be mounted.

An object of the invention is to arrange The invention will be betterunderstood when reference is made to the drawing in which Fig. 1 showsin elevation an improved form of magnetron with a solenoid in crosssection and a schematic diagram of circuits which may be employedtherewith; Figs. 2 and 3 are graphs depicting certain operatingcharacteristics of the magnetron; while Fig. 4 is a top plan view of theelectrode organization.

Referring to Fig. 1, numeral 1 designates a highly evacuated envelopecontaining a cathode in the form of a longitudinally disposed hairpinfilament 2 supported on the upper end by a hook-shaped member 3 whichoverhangs the filament and extends vertically downward to the ress 4.The upright portion of the mem er 3 transversely extending loop 5inorder to offer flexibility to the member, thereby to maintain thefilament 2 taut. The lower ends of the filament are bound to a pair ofupri ht wires 6, 6 sealed in the press and exten ed Ito apair of contactpins 7, 7 securedin the vJase The anodes 9, 9 constitute segments of acylinder and are provided with heat radiat ing fins 10, the anodes beingarranged in an approximate symmetrical manner about the filament 2,leaving a slot or opening 11 on both sides of the filament as shown moreclearly'in Fig. 4. The anodesmay be fabriis provided with a cated in anysuitable manner but I have found I for positioning each electrode in theenvelope.

The rods are fused in presses 17, which tcrminate in a pair of-reentrantstems 18 and are extended through the envelope to connect with externalcircuits. Supported in any suitable manner about the envelope 1, thereis a cylindrical coil or solenoid'19 composed of many turns of wirehaving an out side layer 20 of insulating material such as tape. Thecoil may be energized by a source of direct current (not. shown) throughan ammeter 21 and a variable resistor 22. A source of direct current 23is provided for supplying current to the filament while the anodecurrent may be obtained from a relatively high voltage direct currentsource 24 shown for convenience in the form of a generator. Theanode'circuit also includes a volt meter 25 connected across thegenerator, an ammeter 26 and a current limiting resistance 27 connectedin series. Across the anodes 9, 9 there is connected a high frequencyoscillation circuit commonly called the tank cir cuit and consisting ofan inductance 28 and an adjustable condenser 29 with an ammeter 30 formeasuring tank "or load current. The

- positive side of the source 24 is connected to the inductance,preferably at the mid-tap as shown.

It is apparent that the magnetic lines of force produced by the solenoid19 thread the space between each anode and the filament in a directionparallel to the latter and. it can be shown by operation that whenpotentials of proper magnitude are impressed on theelectrodes andsolenoid, oscillations may be produced in the circuit 28, 29, thefrequency of which is determined by the electrical constants of thecircuit. This frequency may be very high so that the magnetron willgenerate oscillations of exceedingly short wave lengths, for example ofthe order of a few meters or even less than a meter.

Fig. 3 is a graph which depicts exemplary static and dynamiccharacteristics of the split anode type of magnetron. In this figure theordinates represent the values of plate current as measured by themilli-ammeter 26 and also the values of tank or oscillatory current asindicated by the ammeter 30, while the abscissas represent the values ofthe field strength of the solenoid 19 which may be controlled by thevariable resistance 22. .A curve is plotted against each'of the twoordinates and the common abscissa for three typical voltages, 2000, 2500and 3000 applied between the mid-tap of the inductance 28 and thecathode, if the voltage drop in resistance '27 is neglected. In otherwords, there isa pair of curves for each direct current voltage appliedto the anodes, one of the curves showing the relation between theplate'current and field strength and the other of'the pair showing therelationbetween the tank current and the field strength. It will benoted from the graph that no tank or oscillatory current is generated inthe device until the field strength is increased practicall to Qthetheo'reticalcut-ofi value so-called,w ich in the case of the 2000volt curve is in the neighborhood of 115 gausses, in the 2500 volt curveis approximately 130 gausses and in the 3000 volt curve is 145 gausses.The tank currentstarts to flow just before the theoretical cut-off valueis reachedand increases very rapidly at first, then somewhat sloweruntil a maximum is reached, after which the oscillations suddenly cease.

During the generation of oscillations, the operation of the circuits issuch that each of the electrodes 9 constitute a predominantly positivemember for a portion of the time in an alternate manner and if thegreatest tube eiiicicncy is desired it is desirable to constrain theelectron stream as a body to impinge, first on one electrode and then onthe other depending on which is operating for the moment as the anodeproper. It has been found in accordance with my invention that whenhairpin filaments are utilized as a source of electrons in magnetrons ofthls type,

there is a decided difference in efficiency as to the manner in whichthe filament is mounted with respect to the position of the anodes. Itappears that when the plane of the filament is in line with the anodes,i. e. so that a straight tive member contributes little or no electronsto such member. The electrons from this filament leg tend to beattracted to the near.-. est and less positive electrode, hence arelostinsofar as useful current is concerned. I have discovered the mostadvantageous position of a hairpin filament in order to off-set thisdeleterious effect to be directly opposite the slots or openin s betweenthe anodes as clearly shown in lig. 4, i. e. displaced 90 from theposition in lme with the middle portions of the anodes. It is apparentthat under these conditions both filament legs are at substantially thesame distance from each anode and the predominantly positive electrodetends to draw electrons from all portions of-the filament. When thefilament is positioned in accordance with my invention, the electronstream travels more nearly as a complete body toward the electrodemomentarily operating as the anode thus allowing the maximum amount ofcurrent to flow first to one anode and then to the other anode. F 5g. 2graphically shows the advantage of placing the hairpin inline with theslots over theposition of being in line with the anodes. In this figure,curve a which is plotted against tube'eificiency as an ordinate, i. e.

Output in watts Input in watts 1,ase,oea

and at 2300 volts to 35% with correspondin increases throughout theuseful range OI plate voltages, an increase in efficiency ofmore thantwice.

lVhile I have explained my invention more particularly with reference toa hairpin type of filament, it is obvious that the advantages of thediscovery apply to all forms of cathodes which are normallyunsymmetrical and in which one portion of the filament would ordinarilybe in closer proximity to one of the anodes thancto the other.- Theteachings of the present invention clearly show that it'is advantageousto present a line of symmetry for the cathode construction through theslots positioned between the anodes.

\Vhat I claim as new and desire to secure by Letters Patent of theUnitedStates is 1 In a device for generating oscillations, 0 anevacuated envelope containing a cathode, a pluralityofcurvilinear'anodcs separated b oppositely disposed slots and arrangedabout the cathode, an oscillating circuit connected between the anodesand cathode, means for-producing a magnetic field which threads thespace between the anodes and .cathode, means for supplying energy to thecathode and to said circuit, said cathode being constituted of afilament havin a plurality of 4: legs arranged substantially 1n linewith the slots between the anodes,

2. In electron discharge apparatus, an elongated evacuated envelopecontaining a cathode dis osed longitudinally of the envelope,

a plurality of anodes separatedby oppositely disposed slots and arrangedabout the cathode, said anodes comprising segments of a cylinder, atranslatin circuit connected between the anodes and the cathode, saidanodes :a' being constituted of-segments and provided with heatradiating fins, means for producing a magnetic field which threads thespace between the anodes and the cathode, means for supplying energy tothe cathode, to said circuit and to the magnetic field means, saidranged substantially in line with the slots and adapted to cooperatewith the said electrodes, means for producing a magnetic field whichthreads the space between the electrodes and the filament, and means forenergizin the said electrodes and filament.

4. 11 an electron discharge device, ada ted to produce oscillations, anevacuated enve ope containing a filamentary member, a-plurality ofelectrodes separated by oppositely dis osed slots and arranged about thesaid memer, said electrodes comprising segments of a c linder, thefilament being constituted of a p urality of legs arran ed substantiallyin line with the slots and a apted to cooperate with the saidelectrodes, an oscillating circuit connected between said electrodes andthe filament, means for producing a magnetic field which threads thespace between the electrodes and the filament, and means for energizinthe filament and the electrodes.

. 5. An e ectron discharge device comprising an evacuated envelopecontaining a pair of anodes, each of which is of substantially semiclindrical form a solenoid surrounding said evice, said anodes beingarran ed to form a hollow cylinder having a pair 0 diametricallyopposite longitudinal openin s, a cathode located within said cylinderand comprising a pluralit of filament legs arranged substantially inline with said openings, an oscillating circuit connected between saidelec-- trodes and the filament, and separate leading'i in'conductors foreach of said anodes sealed into said envelope. L y

In witness whereof, I have hereunto set my hand this 7th da of October1929.

NNETH d. DE WALT.

cathode being constituted in the form of a hairpin, the legs of whichare arranged substantially in line with the slots between the anodes. y

3. In an electron discharge device, an evacuated envelope containing afilamentary member, a plurality of curvilinear electrodes separated byoppositely disposed slots and arranged about the saidmom er, thefilament 6i being constituted of a plurality of legs ar-

